Tuesday, September 22, 2009

Did Carl Sagan Libel Christiaan Huygens?

"Consider the curious argument by which he deduced the existence on Jupiter of hemp. Galileo had observed four moons traveling around Jupiter. Huygens asked a question of a kind few astronomers would ask today: Why is it that Jupiter has four moons? Well, why does the earth have one moon? Our moon’s function, Huygens reasoned, apart from providing a little light at night and raising the tides, is to aid mariners in navigation. If Jupiter has four moons, there must be as many mariners on that planet. Mariners imply boats; boats imply sails; sails imply ropes. And ropes imply hemp. I sometimes wonder how many of our own prized scientific arguments will appear equally foolish from the vantage of three centuries." (From a Scientific Americanarticle by Carl Sagan)

I came across a reference to this claim in an online conversation and got curious enough to google for it. All of the references I found were suspiciously similar, suggesting that they all were based on the same source. I eventually concluded that the source was Sagan. None of them provided any evidence for the story in anything Huygens had written.

So I want looking and found a webbed translation of Cosmotheoros, a treatise on matters astronomical written by Huygens late in his life. It's an interesting work, combining what appears to be an accurate account of astronomical knowledge of the time with lengthy speculations about possible inhabitants of other planets. Huygens, living more than a century before Darwin, takes it for granted that living creatures are the result of divine design and, logically enough, tries to figure out whether and how a benevolent God would have populated other planets. That seems a bit odd to the modern reader, but the author makes it clear that what he is offering is speculation. There are lots of references to Jupiter and one to hemp, but nothing that even comes close to supporting Sagan's story.

Huygens writes, with reference to Jupiter and Saturn:

"This Position of the Moons, in respect of their Planets, must occasion great many very pretty, wonderful sights to their Inhabitants, if they have any: which is very doubtful, but may for the present be suppos'd."

Which does not sound like a statement from someone with the view of the subject that Sagan attributes to Huygens.

I see three possibilities:

1. I have somehow missed, in Cosmotheoros, the passage on which Sagan bases his story. I think that very unlikely; I haven't read the whole treatise, but it is webbed with a search engine.

2. Sagan is accurately reporting something Huygens wrote elsewhere, perhaps a theory he had rejected by the time he wrote the treatise.

3. Sagan's story is false. Either he is deliberately lying for the sake of telling an entertaining story about how foolish people were in the past or he never bothered to check something he misremembered or got from someone else.

I favor alternative 3, but perhaps one of my readers can provide evidence for one of the others. If the story is based on something Huygens wrote I suspect, after looking through Cosmotheoros, that Sagan is misrepresenting a speculation as a claim.

On page 52, he suggests that they would have rope; on page 56 he says that we have hemp. Could you direct us to where he says that the Jovians have rope made of hemp? (Or anything else made of hemp, or just hemp lying around?) Certainly none of the rope that I personally have is made of hemp.

I saw the reference on p. 56, because I searched for hemp. I misssed the one on page 52.

But it doesn't justified Sagan's story, although it may explain where it came from. Huygens doesn't argue, as Sagan is claiming, that the sailors provide the explanation for the moons. Huygens doesn't claim that people on other planets have hemp, only that they, like us, have useful plants and animals, hemp for rope being offered as an example of one of our useful plants. And he doesn't say anything at all about hemp on Jupiter.

So Sagan, either deliberately to make a better story or inadvertently through trusting to his memory of something he once read, is making Huygens out to be foolish by attributing to him things he didn't say and treating what's obviously speculation as if it was intended to be serious science.

In the 1980 hardcover edition of Cosmos, on page 92, Sagan writes a similar statement about the 17th-century argument for swamps on Venus:

"The absence of anything to see of Venus led some scientists to the curious conclusion that the surface was a swamp, like the Earth in the Carboniferous Period. The argument--if we can dignify it by such a word--went something like this:

'I can't see a thing of Venus.''Why not?''Because it's totally covered with clouds.''What are clouds made of?''Water, of course.''Then why are the clouds of Venus thicker than the clouds on Earth?''Because there's more water there.''But if there is more water in the clouds, there must be more water on the surface. What kind of surfaces are very wet?''Swamps.'"

I'm not sure if the excerpt from Scientific American came before or after Cosmos, but it's possible Sagan was doing a creative copy-and-paste job somewhere...

Someone online, responding to a post of mine, pointed at something else Sagan wrote in which he misrepresented Huygens in a somewhat similar fashion, and explicitly cited Cosmotheoros.

I think it's a fair conclusion that Sagan was referring to that treatise here as well and either didn't bother to make sure what he said was correct or didn't care, since his version made a good story.

One of the great things about the net is that such thinks can be hunted down. Compare with the way the ancient Chinese curse "may you live in interesting times" has been used & reused by writers & journalists criss crossing the world since Robert Kennedy first said it.

Huygens does argue from the existence of moons around Jupiter that there must be many mariners there. He says that the multiplicity of moons would enable the Jovians to have attained seafaring knowledge---with more mastery, in fact, than we have, with our solitary moon. He concludes that the Jovians will have developed sails and ropes and become accomplished seafarers.

At this point, Sagan is already done. He has shown that the scientific arguments of three centuries ago may seem foolish today, and from there he can argue that our contemporary scientific arguments may come to seem equally foolish from a similar perspective.

Why Sagan added that Huygens reasoned directly from Jovian rope to Jovian hemp is a jovial mystery to me.

But Huygens argues that Jupiter will sport a great variety of plants, having forms very similar to those on Earth, and designed specifically by God for the use of his Jovians, who will have forms very similar to ours.

From this general conclusion, a Jovian hemp-like plant follows, because God would provide for his human-like seafaring Jovians as he did for his seafaring Terrans. I would say the corollary was left as an exercise for the reader.

So Huygens would not have considered himself libeled. He would have readily agreed with Sagan about hemp on Jupiter.